The invention is related generally to the field of petroleum wellbore production control apparatus and methods. More specifically, the invention is related to methods and apparatus for controlling production in a deviated wellbore to reduce the possibility of unwanted gas and/or water coning.
Petroleum is produced from an earth formation reservoir when energy stored as pressure in the reservoir fluids is released by exposing the reservoir to a lower pressure in a wellbore drilled through the reservoir. Fluids in the reservoir move into reservoir spaces that were voided by the fluids which moved into the wellbore by expansion against the lower pressure.
Some wellbores are drilled substantially horizontally through certain earth formation reservoirs to increase the wellbore drainage area in the reservoir. Increased drainage area enables the wellbore operator to more efficiently extract petroleum from the reservoir. The typical horizontal wellbore is drilled substantially vertically from the earth""s surface, and is deviated to at or near horizontal where the wellbore is intended to pass through a petroleum bearing interval within the subsurface reservoir.
When petroleum is produced into a horizontal wellbore having a substantial lateral extent from the position of the vertical part of the wellbore, fluid flow from the lateral end of the wellbore (the xe2x80x9ctoexe2x80x9d of the wellbore) is significantly more affected by the friction of fluid flowing inside the wellbore than is the fluid flowing nearer the place at which the wellbore deviates from vertical (the xe2x80x9cheelxe2x80x9d of the wellbore). As a result of the fluid friction, the pressure drop between the reservoir and the wellbore at the toe is typically less than the pressure drop at the heel. This can result in xe2x80x9cconingxe2x80x9d into the wellbore of fluids not desired to be produced from the reservoir. Gas disposed above an oil-bearing interval, for example, may cone into the wellbore, or water disposed below an oil bearing or a gas bearing interval in the reservoir may cone into the wellbore. In any case, the possibility of coning reduces the productive capacity of a horizontal wellbore by reducing the overall fluid flow rate which may be attained.
Methods and apparatus known in the art for reducing coning are described, for example in U.S. Pat. No. 5,803,179 issued to Echols and U.S. Pat. No. 5,435,393 issued to Brekke et al. The apparatus known in the art include hydraulically segmenting the exterior of the wellbore along its length in the horizontal section. Each segment is placed into hydraulic communication with the reservoir independently through a flow controlling device having a selected restriction to fluid flow. Typically, the selected flow restriction is more resistant to flow in the controlling devices positioned near the heel of the well, and is lower in the flow control devices positioned near the toe of the well. The purpose of the selected flow restrictions is to more evenly distribute pressure drop between the reservoir and the wellbore along the length of the wellbore. More evenly distributed pressure drop can reduce the possibility of coning.
Most of the apparatus and methods known in the art for controlling flow into a horizontal wellbore rely on fixed flow restrictors. While the restriction provided by each individual flow restrictor can be selected initially to produce a substantially evenly distributed pressure drop along the wellbore, once the apparatus is installed in the wellbore, the restrictions cannot be adjusted. If there are any changes in the character of the fluid flow along the wellbore, the amount of pressure drop at one or more of the fixed flow restrictors may not be suitable for the existing fluid flow to provide an evenly distributed pressure drop along the wellbore. Certain throttling devices also have been proposed to help the flow. Such devices use a spring biased member that moves to restrict flow when the pressure drop increases. Such devices, however, are somewhat limited in compensating for changes in the reservoir. An example of such a character change can be as simple as a change in the total fluid flow rate through the wellbore. Other types of changes in fluid flow character can have similar effects on the ability of prior art apparatus and methods to evenly distribute flow along a horizontal wellbore.
Accordingly, there is a need for an apparatus and method which can evenly distribute flow along a horizontal wellbore and which can respond to changes in the character of flow along the wellbore.
One aspect of the invention is an apparatus for controlling fluid production in a horizontal wellbore. The apparatus includes a flow pipe the interior of which is in hydraulic communication with the earth""s surface. The flow pipe is disposed in a substantially horizontal portion of the wellbore. A plurality of flow control valves are disposed at spaced apart positions along the length of the flow pipe. Each of the valves provides hydraulic communication between the interior of the pipe and a fluid reservoir in an earth formation. Each of the valves is adapted to maintain a substantially constant pressure drop between the reservoir and the interior of the flow pipe.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.